The present invention relates to a heater for top portions of containers, and more particularly to a heater for containers each having an open upper end and filled with contents such as milk for use in folding the top portions of the containers to the shape of a gabled roof and heat-sealing the top portions.
FIG. 5 shows such a heater already known for use with containers 91 filled with contents and each having a top forming tubular portion 92 generally square in cross section for heating seal parts of the top forming portion with hot air which parts are to be heat-sealed. The heater comprises a hot air nozzle 93 in the form of a bottomed tube having a generally square cross section and to be inserted into the top forming portion 92 for heating. The hot air nozzle 93 has first to fourth four side walls 94 integral with one another with a ridgeline formed between the adjoining side walls. The side walls 94 are vertical and formed with orifices 95 as distributed over the regions thereof corresponding to the respective seal parts.
With the conventional heater, hot air is forced out from the nozzle 93 against the seal portions to heat these portions, whereupon the air changes its course, partly turning upward to flow out of the container 91. The rest of the air flows downward in the interior of the container. The downward flow of hot air forces up a portion of the liquid filled in the container which portion has been bubbled up when the liquid is placed into the container. Such bubbles will then adhere to the bottom surface of the nozzle 93 and will be scorched with the heat of the nozzle 93 to form an accumulation. The accumulation falls off from time to time and becomes incorporated into the contents, affording an unacceptable product.
The adhesion of bubbles can be obviated by reducing the rate of discharge of hot air, but an impaired heat pattern will then result to produce faulty seals.